Mufflers are known in a variety of types. For example, there are such which operate on the principle of absorption muffling, with the exhaust being supplied by means of pipes formed in their circumference with holes through which the pressure wave can exit uniformly distributed and by means of rock wool surrounding these tubes is muffled to a certain extent. These absorption mufflers are used for example as main mufflers (e.g. DE-OS No. 22 57 854)--also called subsidiary mufflers--in order to particularly muffle the high frequency noise portion of the exhaust gases. In order to obtain a stronger muffling, preliminary mufflers are frequently added to the main muffler (e.g. DE-OS No. 22 57 852). Due to the rock wool filling of the known absorption mufflers a comparatively good muffling effect is obtained. Rock wool is a relatively long-fibered mass which over a period of time is destroyed by the high-frequency component of the pressure wave of the exhaust gases, so that a flour-like residue is obtained. Due to to underpressure existing in the pipe as a result of the out-flowing exhaust gases this flour is entrained and transported to the exterior, which is highly undesirable. Added to this is the fact that the muffler gradually loses its intended function as the destruction of the rock wool proceeds.
For this reason reflection mufflers have become known besides the absorption-type mufflers. Here, analogous to the absorption type mufflers, the exhaust gas passes an "inlet shower" (body with a plurality of outlet openings) into reflection chambers and is then directed via different tubes into diverse additional reflection spaces where the exhaust gas again can escape via outlet openings (e.g. perforated pipes) to finally flow to the exterior the exhaust gas outlet pipe.
The principal used in the reflection-type mufflers thus resides in the fact that the noise is reflected in the reflection chambers by the gas direction and thus is muffled in part by the superposition and the respective outlet from the plurality of small openings into the reflection chamber, particularly with reference to the high frequency noise component.
Disadvantageous in these known mufflers are the transitions between the pipes and the reflection chambers, which results in a high flow resistance and thus back pressure to the engine. Beyond this, only certain frequencies which depend upon the dimensions of the muffler, can be effectively muffled. In particular, high-frequency components are poorly muffled. To avoid restricting the power of the engine too much, it is necessary for obtaining a better flow of the exhaust gases to select the cross section of the pipes relatively large. Since the pipes are, however, guided within the reflection chambers the space necessary for the reflection in the chambers is too small, which in turn results in a poor muffling of the low-frequency noise component. For this reason, the dimensions of the conventional reflection chambers must be made larger. This requires a larger overall dimension of the muffler, so that a compact muffler, as it is for example possible with the absorption-type mufflers, cannot be produced, aside from the higher material requirements which makes these known reflection type mufflers more expensive. Finally, the muffler pot constitutes a hollow body in which the pipes are guided and which air is excited to resonate by their vibrations, which causes disadvantageous radiation noises that do not exist in absorption type mufflers because of the rock wool filling. These disadvantageous noises can be overcome only with large structural expenditures, which again correspondingly are reflected in the manufacturing costs. The task of the invention is to provide a muffler according to the preamble of the claim 1 with good damping effect over as large as possible a frequency range, particularly high-frequency noise proportion without increased losses at small structural size and low body noise radiation.
The plurality of mutually parallel intermediate channels has by comparison to the cross-section of the exhaust gas inlet pipe a large total cross-section, so that the inflowing of the exhaust gases from the first outer reflection chamber into the intermediate channels causes only a very small flow resistance. Because of this only practically negligible losses in efficiency of the combustion engine are observed. Added to this is the fact that good muffling of the high-frequency noise component is obtained in that the wall surface of all channels combined is larger by a multiple than in the known constructions. One obtains a correspondingly high friction value and a good radiation into the reflection chambers, which is advantageous for muffling low-frequency noise components. In contradistinction to the state of the art, the muffling thus is effected in the first line not by the gas transmission from the pipe to the reflection chamber, but by the inventively provided plurality of intermediate channels themselves. Due to the large number of these relatively narrow intermediate channels the volume of the reflection chambers also is not so strongly reduced, so that the still available reflection chamber volume advantageously influences the muffling effect. According to the invention it is thus not necessary, in contradistinction to the state of the art, to increase the size of a muffler constructed in accordance with the invention, in order to muffle low-frequency noise components; nevertheless, a large friction surface is made available for muffling higher-frequency noise components without causing an increase in the efficiency loss of the combustion engine.